use_late_for_private_fields_and_variables

Use 'late' for private members with a non-nullable type.

The analyzer produces this diagnostic when a private field or variable is marked as being nullable, but every reference assumes that the variable is never null.

The following code produces this diagnostic because the private top-level variable _i is nullable, but every reference assumes that it will not be null:

void f() {
  _i!.abs();
}

int? _i;

Mark the variable or field as being both non-nullable and late to indicate that it will always be assigned a non-null:

void f() {
  _i.abs();
}

late int _i;